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Confined Space Hazards

• The hazards encountered and associated with entering and working in confined spaces are capable ofcausing bodily injury, illness, and death to the worker. • It should always be considered that the most unfavorable situation exists in every confined space and thatthe danger of explosion, poisoning, and asphyxiation will be present atthe onset of entry. • Before forced ventilation is initiated, information such as restricted areas within the confined space, voids, the nature ofthe contaminants present, the size ofthe space, the type ofwork to be performed, and the number of people involved should be considered. • The ventilation air should not create an additional hazard due to recirculation of contaminants, improper arrangement ofthe inlet duct, or by the substitution of anything otherthan fresh (normal) air (approximately 20.9% oxygen, 78.1% nitrogen, and 1% argon with small amounts ofvarious other gases). • The terms air and oxygen are sometimes considered synonymous. However, this is a dangerous assumption, since the use of oxygen in place offresh (normal) air for ventilation will expand the limits offlammability and 

# I Increase the hazards offire and explosron**-----~**


# Types ofConfined Spaces

• Confined spaces can be categorized generally as those with open tops and with a depth that will restrictthe natural movement ofair, and enclosed spaces with very limited openings for entry. (In either case, the space may contain mechanical equipment with moving parts.) • Degreasers, pits, and certain types ofstorage tanks may be classified as opentopped confined spaces that usually contain no moving parts. However, gasesthat are heavierthan air (butane, propane, and other hydrocarbons) remain in depressions and will flowto low points where they are difficultto remove. • Other hazards may develop dueto the work performed inthe confined space or because of corrosive residues that accelerate the decomposition ofscaffolding supports and electrical components. o Confined spaces such as sewers, casings, tanks, silos, vaults, and compartments ofships usually have limited accesswhich increasesthe risk of injury. ----------

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## Types ofConfined Spaces (cont'd)

• Hazards specificto a confined space are dictated by: 1. the material stored or used in the confined space; as an example, damp activated carbon in a filtration tankwill absorb oxygen, thus creating an oxygen deficient atmosphere; 2. the activity carried out, such as the fermentation ofmolassesthat creates ethyl alcohol vapors and decreasesthe oxygen content ofthe atmosphere; or 3. the external environment, as in the case of sewer systems that may be affected by high 

### tides, heavierthan air gases, or flash floods. • The most hazardous kind ofconfined space is the type that combines limited access and mechanical devices. Digesters and boilers I usually-contain power-driven equipme.nt. I 

### which, unless properly isolated, may be inadvertently activated afterentry.

# ~e~sons for Entering

# Confined~paces

I ll • 

### Usually doneto perform a necessaryfunction, such as inspection, repair, maintenance 

### (cleaning or painting), or similaroperations whichwould be an infrequentor irregular function ofthetotal industrial activity. • Entry may also be made during new construction. When the area meetsthe criteria for a confined space, all ventilation and other requirements should be enforced. • One ofthe mostdifficultentries to control is that of unauthorized entry, especiallywhen there are large numbersofworkers and trades involved, such as welders, painters, electricians, and safety monitors. • A final and most important reason for entry would be emergency rescue. The standby person and all rescue personnel should be aware ofthe structural design ofthe space, emergency exit procedures, and life support systems required. ----·-----

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Flammable Atmospheres

• Generally arisefrom enriched oxygen atmospheres, vaporization offlammable liquids, byproducts ofwork, chemical reactions, concentrations ofcombustible dusts, and desorption ofchemical from inner surfaces of the confined space. • Flammable gases such as acetylene, butane, propane, hydrogen, methane, natural or manufactured gases or vapors from liquid hydrocarbons can be trapped in confined spaces, and since many gases are heavier than air, they 

### will seek lower levels as in pits, sewers, and various types ofstorage tanks and vessels. • In a closed top tank, lighterthan airgases may rise and develop a flammable concentration iftrapped abovethe opening. • The byproducts ofwork procedures such as spray 

### painting can generate flammable orexplosive conditions within a confined space. • Welding in a confined space is a major cause of explosions in areasthat contained combustible gas. • Combustible dust concentrations are usuallyfound during the process ofloading, unloading, and conveying grain products, nitrated fertilizers, finely ground chemical products, and any other combustible material.



# Toxic Atmospheres

• The sources oftoxic atmospheres encountered in confined spaces may arise from the following: 1. The manufacturing process (for example, in producing polyvinyl chloride, hydrogen chloride is used as will as vinyl chloride monomer, which is carcinogenic). 2. The product stored [removing decomposed organic material from a tank can liberatetoxic substances, such as hydrogen sulfide (H,S)]. 3. The operation performed in the confined space (for example, welding orbrazing with metals capable of producingtoxic fumes). • During loading, unloading, formulation, and production, mechanical and/or human error may also producetoxic gaseswhich are notpartofthe planned operation. • Carbon monoxide (CO) is a hazardous gasthat may build up in a confined space.

Odorless, colorless gas approximatelythe same density as air is formed from incomplete combustion of organic materials such aswood, coal, gas, oil, and gasoline; can be formed from microbial decomposition oforganic matter in sewers, silos, and fermentation tanks.

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Toxic Atmospheres (cont'd)

• Early stages ofCO intoxication are nausea and headache. May be fatal at 1000 ppm in air, and is considered dangerous at200 ppm, because it forms carboxyhemoglobin in the blood which prevents the distribution ofoxygen in the body. • A safe reading on a combustible gas indicator does not ensurethat CO is not present. Carbon monoxide must betested for specifically. • Theformation ofCO may result from chemical reactions orwork activities, thereforefatalities dueto CO poisoning are not confined to any particular industry. Examples: • Sewage treatment plants due to decomposition products and lack ofventilation in confined spaces • Formation ofsilo gas in grain storage elevators



# Irritant (Corrosive) Atmospheres

• Irritant orcorrosive atmospheres can be divided into primary and secondary groups. • The primary irritants exert no systemictoxic effects (effects on the entire body). Examples include chlorine, ozone, hydrochloric acid, hydrofluoricacid, sulfuric acid, nitrogen dioxide, ammonia, and sulfur dioxide. • A secondary irritant is onethat may produce systemic toxic effects in addition to surface irritation. Examples include benzene, carbon tetrachloride, ethyl chloride, trichloroethane, trichloroethylene, and chloropropene. • Irritant gases varywidely among all areas ofindustrial activity. They can befound in plastics plants, chemical plants, the petroleum industry, tanneries, refrigeration industries, paint manufacturing, and mining operations. • Prolonged exposure at irritant or corrosive concentrations in a confined space may produce little or no evidence of irritation but may result in a general weakening ofthe defense reflexes from changes in sensitivity. The danger in this situation is thatthe

, worker is usually not aware ofany increase in his/her 

# L exposure to toxic substances. --···----------------

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Asphyxiating Atmospheres

• The normal atmosphere is composed approximately of20.9% oxygen, 78.1% nitrogen, and 1% argon with small amounts ofvarious other gases. • Decreased oxygen levels (belowthe atmospheric level of20.9% by volume) can cause various effects including: • Level of 17%: increased breathing volume and accelerated heartbeat • Between 14-16%: increased breathing volume, accelerated heartbeat, very poor muscular coordination, rapid fatigue, and intermittent respiration • Between 6-10%: nausea, vomiting, inabilityto perform, and unconsciousness Lessthan 6%: spasmatic breathing, convulsive movements, and death in minutes



# I Asphyxiating Atmospheres-(cont'd) I
• Reduction ofoxygen in a confined space may bethe result ofeitherconsumption ordisplacement. • Consumption ofoxygen: Takes place during combustion offlammable substances, as in welding, heating, cutting, and brazing During bacterial action, as in the fermentation process During chemical reactions as in the formation ofrust on the exposed surface ofthe confined space (iron oxide) • Rate ofconsumption influenced by the number of people working in a confined space and the amount of their physical activity • Displacement ofoxygen byanothergas: Examples ofgasesthat are used to displace air, and therefore reduce the oxygen level, are helium, argon, and nitrogen. Carbon dioxide may also be used to displace airand can occur naturally in sewers, storage bins, wells, tunnels, wine vats, and grain elevators. Gases such as nitrogen, argon, helium, and carbon dioxide are used as inerting agentsto displace flammable substances and retard pyrophoric reactions. resulting in oxygen deficient atmospheres. -----·--



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# General Safety Hazards Mechanical

• Ifactivation ofelectrical or mechanical equipmentwould cause injury, each piece ofequipmentshould be manually isolated to prevent inadvertentactivation before workers enterorwhile they work in a confined space. • To preventvapor leaks, flashbacks, and other hazards, workers should completely 

## isolate the spaee. • The closing ofvalves is not sufficient
- all pipes must be physically disconnected or isolation blanks bolted in place. • Where flammable liquids orvapors may re-contaminate the confined space, the blanked ordisconnected pipes should be inspected and tested for leakage. 

### • Other areas ofconcern are steam valves, pressure lines, and chemical transfer pipes.



# General Safety Hazards Communication Problems

• Communication between the worker inside and the standby person outside is ofutmost importance. • When visual monitoring ofthe worker is not possible because ofthe design ofthe confined space or location ofthe entry hatch, a voice oralarm-activated explosion prooftype ofcommunication system will be necessary. • Suitable illumination ofan approved type is required to provide sufficientvisibility for work in accordancewith the recommendations made in the Illuminating Engineering Society Lighting Handbook.**-----~** ------ , __**~--** ..

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# General Safety Hazards Entry and Exit

• Entry and exittime is ofmajor significance as a physical limitation and is directly related to the potential hazard ofthe confined space. • The extentofprecautions taken and the standby equipment needed to maintain a safe work area will be determined by the means ofaccess and rescue. • The following should be considered:

• Type ofconfined space to be entered • Access to the entrance • Numberand size ofopenings • Barriers within the space Occupancy load • Time requirement for exiting in event offire or vapor incursion • Time required to rescue injured workers



# Physical Hazards Thermal Effects

• When a body temperature ofapproximately 102F is exceeded, workers are less 

## efficient, and are prone to heat exhaustion, heat cramps, or heat stroke. • Special precautions must be taken in cold environments to preventfrostbite, trench foot, and general hypothermia. • Protective insulated clothing for both hot and cold environmentswill add additional bulk to the worker and must be considered in allowing for movement in the confined space and exittime. ------------· --

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# Physical Hazards Noise

• Noise problems are usually intensified in confined spaces because the interiortends to cause sound to reverberate and thus expose the workerto higher sound levels than those found in an open environment. • This intensified noise increases the risk of hearing damage to workers which could result in temporary or permanent loss of hearing. • Noise in a confined space which may not be intense enough to cause hearing damage may still disruptverbal communication with the emergency standby person on the exterior ofthe confined space.**~-**


# Physical Hazards Vibration

• Whole bodyvibration may affect multiple body parts and organs depending upon the vibration characteristics. • Segmental vibration, unlike whole body vibration, appears to be more localized in creating injuryto the fingers and hands of workers using tools, such as pneumatic hammers, rotary grinders or other hand tools which cause vibration. 

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# Physical Hazards General/Physical

• Some physical hazards such as scaffolding, surface residues, and structural hazards cannot be eliminated because ofthe nature ofthe confined space orthe work to be performed. • The use ofscaffolding in confined spaces has contributed to many accidents caused by workers or materials falling, improper use ofguard rails, and lack of maintenance to insure worker safety. • Surface residues in confined spaces can increase the already hazardous conditions ofelectrical shock, reaction of incompatible materials, liberation oftoxic substances, and bodily injury dueto slips and falls. Without protective clothing, additional hazards to health may arise due to surface residues. • Structural hazardswithin a confined space such as baffles in horizontal tanks, trays in vertical towers, bends in tunnels, overhead structural members, orscaffolding installed for maintenance constitute physical hazards, which are exacerbated by the physical surroundings. • Rescue procedures may require withdrawal of an injured or unconscious person. Careful planning must be given to the relationship between the internal structure, the exit opening, and theworker.